In underground mining in general, and in coal mining specifically, there is constant and well deserved attention paid to supporting the mine roof. There are a variety of ways in which roof support may be effected in "conventional" mines as well as in those mines which employ mining methods described as short wall and/or long wall mining. In "conventional" mines support is usually provided to a previously unsupported (and usually just mined) area of mine roof through conventional roof bolts and the like. These bolts are inserted into substantially vertically drilled holes into the mine roof by a bolter apparatus and generally have shapes, designs and lengths which depend, as least to a large extent upon the geographical makeup of the mine, the coal being mined, and the mine roof. The roof bolts with conventional, expandable, wedge-type members and bearing plates, as well as the "less conventional" and "newly" introduced resin bolts, tie the overhead strata together, thereby reducing and hopefully eliminating the possibility of roof falls. In the areas of conventional mining, where large blocks of coal are dislodged from the coal face, it is necessary to place these roof bolts along predetermined rows and files throughout the length and width of substantially all of the mined area. Moreover, there are federal, state and county regulations which stipulate exactly how much length of unsupported mine roof may be present between the last roof bolt and the coal face. These regulations are strictly followed by mine personnel because of the relationship between roof falls and unsupported mine roof areas between the last row of bolts and the face being mined. The gamble of men and equipment is far too great to extract coal and support the mine roof in any other way within "conventional" mining environments.
Under current mining regulations it is necessary, subsequent to the extraction of coal from the face, to move a portable self-propelled bolter vehicle into the haulageway and set both rows and files of roof bolts into the mine roof to reduce the length of unsupported roof. Generally, the maximum length of allowable unsupported roof is approximately twenty feet. When such a length has been reached, the coal miner is extracted and the bolting operation commences for that given area. The roof bolts which are set into the predrilled holes in the mine roof have center to center premissible distances of four feet with a maximum four-foot distance between the rib and the next inward bolt. Roof bolting machines currently available must drill and set successive series (usually three or four) of roof bolts (having a width of between two and four roof bolts) across the longitudinal axis of the haulageway, continuing down the haulageway until four rows have been set and the roof is again supported. Each of these successive lateral drilling series necessitates the retraction of temporary roof supports, the movement or tramming of the drilling vehicle four feet further into the passage and the positioning of the drilling machine so that the next series of holes drilled will be four feet from the last.
The drilling operation itself includes the steps of rotating the drill steel and drill head as well as providing the necessary upward thrust to the two in order to effect proper drilling into the mine roof. After the drilling operation has been accomplished for a given bolting vehicle position (usually four holes drilled by two drilling units), the vehicle is moved or trammed to another location where drilling is desired. For the most part, these functions are almost always hydraulically powered, although exceptions do occur.
The currently available roof drilling and bolting apparatus employ a plurality of hydraulic pumps and hoses to carry sufficient hydraulic fluid to the hydraulically actuated motors, jacks and other elements necessary for the proper operation of a roof bolting machine. The inclusion of the numbers of such equipment into such vehicles results in a complicated, expensive mechanism which is more difficult to maintain. The pumps and other hydraulic elements of these systems generally have limited use inasmuch as they are utilized only during the operation of the very specific element they are designed to power. The currently available hydraulic systems are cumbersome, expensive and inefficient both in terms of the amount of equipment and its power usage.